/Engine/Plugins/Runtime/MeshModelingToolset/Source/ModelingComponents/Public/Selection/StoredMeshSelectionUtil.h
Note this way of identifying edges will still not be stable in the case of triangles being reinserted with rotated indices (e.g. a triangle "a, b, c" reinserted as "b, c, d"). Storing Vid pairs would be necessary to be robust to that case, but finding an edge from vertices is a slower operation compared to the constant-time tri/index lookup used here.
class FMeshEdgesFromTriangleSubIndices